If you're talking building a legitimate 73-key MIDI controller that's superior to what's commercially available, unless you have a machine-shop and the skills to go along with that, it's probably not going to go well.

If you like to tinker, have the skills it is probably possible. For me it would be like attempting to hitch hike to Africa and live to tell the story.If your goal is to actually make music in a studio I would discourage it.